摘要
Anion (X) recognition fluorescent chemosensor 5-(4-Fluoro-phenyl)-2-hydroxy-nicotinonitrile (FP2HN) having both -NH and -OH groups in its two tautomeric forms has been synthesized and its excited state intramolecular proton transfer (ESIPT) reaction has been investigated by UV-vis, fluorescence, 1H NMR spectroscopy in combination with computational calculations. The experimental findings show that FP2HN selectively recognizes F鈭?/sup>, AcO鈭?/sup> and H2PO4鈭?/sup> ions through the formation of -N(O)H鈰疿 hydrogen bonding (HB) complex. The binding constant obtained by non-linear fit predicts the binding order of F鈭?/sup> > AcO鈭?/sup> > H2PO4鈭?/sup> > Cl鈭?/sup>. The ESIPT process of FP2HN is inhibited either by the fluoride induced deprotonation of acidic proton of FP2HN or by the formation of a strong -N(O)H鈰疿 intermolecular hydrogen bonding complex. Further insights into the recognition mechanism of the receptor-anion complexes using ab initio calculations have been performed which support the experimental binding affinity order of F鈭?/sup> > AcO鈭?/sup> > H2PO4鈭?/sup> > Cl鈭?/sup>.